Boric acid free flux

ABSTRACT

The invention described herein pertains generally to boric acid free flux composition wherein in some embodiments, a phthalocyanine pigment is used to effect a color change at activation temperature.

PRIORITY

The present application is a divisional of U.S. patent application Ser.No. 13/838,485, filed on Mar. 15, 2013, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The invention described herein pertains generally to boric acid freebrazing flux compositions.

BACKGROUND OF THE INVENTION

Per the Regulation (EC) No 1272/2008 of the European Parliament and ofthe Council on classification, labeling and packaging of substances andmixtures“boric acid (a component of most brazing fluxes), is classifiedas a reproductive toxin in the European Union. This requires speciallabeling, leading to an effort on the part of consumers to look forboric acid free alternatives. Suitable boric acid free brazing fluxesmust be developed to maintain market share and meet consumer demand.

Brazing is a thermal process, similar to soldering for joining metallicstock materials (hereinafter referred to as base metal), wherein aliquid phase is obtained by melting only the brazing metallic material(hereinafter referred to as filler metal) at temperatures exceeding 450°C. (840° F.). The solidus temperature of the base metal is not reachedduring this process. Filler metals can be alloys or pure metals.

Assuming pure metal surfaces, the liquid filler metal is able to spreadin a thin layer on the base metal surface, wetting it. The filler metaladheres to the base metal surface by a slight alloying of the base andfiller metals. The filler metal spreads out over the joint surface and,after solidifying, forms a loadable joint with the base metal.

If designed in a manner suitable for brazing, the two joint surfaces ofthe parts to be joined form a narrow parallel slit, or capillary. Themolten filler metal then flows of its own accord into this slit due tothe capillary action, filling said slit. The minimum temperature on thesurface of the component to be brazed at which said process takes placeundisturbed is the so-called working temperature. It is a characteristicquantity for the filler metal in question.

In order to be able to form a bond with the base metal, the moltenfiller metal must come into direct contact with the base metal. Oxidelayers of the kind present on any engineering metal surface must thus beloosened first and removed. If brazing takes place in the air, this isachieved by covering the brazing site with fluxes in the melt flow ofwhich the oxides dissolve, are reduced or decompose at and above theactive temperature of the flux.

The flux thus primarily has the task of removing oxides present on thefiller and base metal surfaces and preventing them from re-formingduring the brazing process so that the filler metal is able to wet thebase metal sufficiently.

The melting point and the effective temperature of the fluxes must bematched to the working temperature of the brazing filler metal used,whereby the flux should melt at about 50-100° C. below the workingtemperature of the filler metal used and become fully effective fromthis temperature onwards. Moreover, the molten flux should form a dense,uniform coating on the workpiece which remains intact at the requiredbrazing temperature and for the duration of the brazing period.

Brazing fluxes are composed substantially of salt mixtures which, in themolten state, are capable of dissolving metal oxides. These fluxes aresubstantially inorganic boron compounds such as, in particular, alkaliborates and fluoroborates, including boric acid, and halides such as, inparticular, an alkali halide; e.g. alkali fluorides.

At least one aspect of the invention resides in the superior ability toachieve desirable flux characteristics without the presence of boricacid (H₃BO₃) or borax (NaB₄O₅(OH)₄.H₂O) in the flux.

SUMMARY OF THE INVENTION

The invention describes various flux compositions which do not containboric acid, and which optionally include a color change pigment atactivation temperature, e.g., a phthalocyanine pigment.

These and other objects of this invention will be evident when viewed inlight of the detailed description and appended claims.

DETAILED DESCRIPTION OF THE INVENTION

The best mode for carrying out the invention will now be described forthe purposes of illustrating the best mode known to the applicant at thetime of the filing of this invention. The examples are illustrative onlyand not meant to limit the invention, as measured by the scope andspirit of the claims.

As used herein, the term “approximately” means within the stated rangeswith a tolerance of 10%.

The present brazing flux composition is boric acid free, provides goodwetting characteristics and changes color from a color in the visiblespectrum to clear at activation temperature.

The invention will now be described in a series of non-limiting, butillustrative examples.

Example #1

In one embodiment of the invention, a black high temperature paste fluxis described, the composition of which includes a mixture of water,potassium bifluoride, boron, udylite and fumed silica in the followingweight percentages.

TABLE 1 High Temperature Boric Acid Free Paste Flux Component WeightPercentage Water balance Udylite (wetting agent 62) 0.25-0.50% wettingagent/surfactant Potassium bifluoride (KHF₂) 12.4-16.8% etchant/cleanbase metal surface Fumed silica (SiO₂) 0.71-1.35% emulsifyingagent/plasticizer Potassium tetraborate (K₂B₄O₇•4H₂O) 29.5-34.8%dissolve metallic oxides and protect brazing surface from oxidationPotassium fluoroborate (KBF₄) 29.5-34.8% dissolve metallic oxides andhalides and protect brazing surface from oxidation Boron 0.50-0.98%protect surface from oxidation at high brazing temperatures

Example #2

In another embodiment of the invention, a low temperature boric acidfree paste flux will include a mixture of water, potassium bifluoride,potassium tetraborate, potassium fluoroborate, pigment, Udylite andfumed silica in the following weight percentages.

TABLE 2 Low Temperature Boric Acid Free Paste Flux Component WeightPercentage Water balance Udylite (wetting agent 62) 0.25-0.50% wettingagent/surfactant Potassium bifluoride (KHF₂) 12.4-16.8% etchant/cleanbase metal surface Fumed silica (SiO₂) 0.71-1.35% emulsifyingagent/plasticizer Potassium tetraborate (K₂B₄O₇•4H₂O) 29.5-34.8%dissolve metallic oxides and protect brazing surface from oxidationPotassium fluoroborate (KBF₄) 29.5-34.8% dissolve metallic oxides andhalides and protect brazing surface from oxidation Pigment(phthalocyanine) 0.25-0.98% active temperature indicator

Example #3

In another embodiment of the invention, a high temperature boric acidfree powder flux will include a mixture of potassium tetraborate,potassium fluorosilicate, potassium fluoroborate and boron in thefollowing weight percentages.

TABLE 3 High Temperature Boric Acid Free Powder Flux Component WeightPercentage Potassium tetraborate (K₂B₄O₇•4H₂O) 46.2-51.6% dissolvemetallic oxides and protect brazing surface from oxidation Potassiumfluorosilicate (K₂SiF₆) 1.20-1.99% wetting agent/surfactant PotassiumFluoroborate (KBF₄) 46.2-51.6% dissolve metallic oxides and halides andprotect brazing surface from oxidation Boron 0.85-1.02% protect surfacefrom oxidation at high brazing temperatures

Example #4

In another embodiment of the invention, a low temperature boric acidfree powder flux will include a mixture of potassium tetraborate,potassium fluorosilicate, potassium fluoroborate and a pigment in thefollowing weight percentages.

TABLE 4 Low Temperature Boric Acid Free Powder Flux Component WeightPercentage Potassium tetraborate (K₂B₄O₇•4H₂O) 46.2-51.6% dissolvemetallic oxides and protect brazing surface from oxidation Potassiumfluorosilicate (K₂SiF₆) 1.20-1.99% wetting agent/surfactant PotassiumFluoroborate (KBF₄) 46.2-51.6% dissolve metallic oxides and halides andprotect brazing surface from oxidation Pigment (phthalocyanine 500-600°C.) 0.50-0.98% active temperature indicator

As described above, the phthalocyanine pigment is an aromaticmacrocyclic compound that forms coordination complexes with manyelements of the periodic table. These complexes are intensely coloredwhich facilitates the color transformation at temperatures employed inthe reaction. As described above, the phthalocyanine pigment is anaromatic macrocyclic compound that forms coordination complexes withmany elements of the periodic table. These complexes are intenselycolored which facilitates the color transformation at temperaturesemployed in the reaction from colored in the visible spectrum toessentially colorless at temperature. The phthalocyanine macrocycliccompound is illustrated below, and wherein a metallic ion would becoordination bonded to the nitrogen atoms, typically within the5-membered rings.

The above compositions are useful for the brazing of metallic materialsbased on copper, silver, nickel and iron based alloys. Without beingheld to any one theory or mechanism of operation, the flux is used toremove the oxide layer and enable the wetting of the base materials. Theactivated flux creates a layer on the workpiece and removes any surfaceoxides. The color change at activation temperature is a distinctcharacteristic not seen when compared to fluxes commercially availablefor purchase.

The four classes of fluxes were tested and met all AWS A5.31M/A5.31:2012testing standards for water content, particle, adhesion, fluidity,fluxing action, flow, life and viscosity.

The boric acid free fluxes described in Tables 1-4 deliver excellentperformance, standing on their own as brazing fluxes. As discussedbelow, the boric acid free fluxes deliver results often superior tocommercially available standard fluxes that are not boric acid free. Thefollowing tests were performed.

Oxide Removal

All of the boric acid free fluxes in Tables 1-4 dissolved all oxidesfrom the base metal surface. The paste fluxes outperformed commerciallyavailable EASY-FLO® flux, which contains boric acid, having a registeredoffice at Johnson Matthey Plc., 5th Floor 25 Farringdon Street, LondonEC4A 4AB, United Kingdom.

Activation Range

All of the boric acid free fluxes in Tables 1-4 are fully active,removing oxides, throughout the range of 1050° F.-1600° F. (566° C.-871° C.) and 1050° F.-1800° F. (566° C. - 982° C.), for the low temperature(green) flux and the high temperature flux (black) respectively.

The powder fluxes outperformed commercially available EASY-FLO® flux,which contains boric acid, commercially available from Johnson MattheyPlc. and having a registered office at 5th Floor 25 Farringdon Street,London EC4A 4AB, United Kingdom, as well as BRAZETEC® flux, commerciallyavailable from Umicore AG & Co. KG, Business Line BrazeTec, RodenbacherChaussee 4, 63457 Hanau Wolfgang, Germany.

Hot Rodding

“Hot Rodding” is the coating of a piece of brazing rod (filler metal) bydipping a hot end into a powdered flux. The boric acid free fluxes inTables 1-4 coated 22% better than a commercially available powder flux,STTS Flux IT 340 M, available from STTS Brazing Solutions, Z.A.E. laNeuvillette 60240 Fleury (France).

Flux Flowability in Activation Range

A flowability test, AWS FB3-K, was performed per AWS A5.31M/A5.31:2012.Flowability was good for both the powder and the paste fluxes for theboric acid free fluxes in Tables 1-4. The paste flux flowabilty wassuperior, outperforming commercially available EASY-FLO® flux, whichcontains boric acid, commercially available from Johnson Matthey Plc.,having a registered office at 5th Floor 25 Farringdon Street, LondonEC4A 4AB, United Kingdom.

Brazing Odor and Fumes

There was very little objectionable odor and fumes throughout thebrazing process for all of the boric acid free fluxes in Tables 1-4. Thepowder flux had significantly less odor than that of the Castolin boricacid containing flux, which was tested, commercially available fromCastolin Eutectic International.

Activation Indicator

The pigmented fluxes of Tables 2 & 4 were the only fluxes that has avisual indicator of activation temperature.

The invention has been described with reference to preferred andalternate embodiments. Obviously, modifications and alterations willoccur to others upon the reading and understanding of the specification.It is intended to include all such modifications and alterations insofaras they come within the scope of the appended claims or the equivalentsthereof.

What is claimed is:
 1. A boric acid free paste flux composition whichcomprises the following components: water balance a wetting agent0.25-0.50% potassium bifluoride (KHF₂) 12.4-16.8% fumed silica (SiO₂)0.71-1.35% potassium tetraborate (K₂B₄O₇•4H₂0) 29.5-34.8% potassiumfluoroborate (KBF₄) 29.5-34.8% pigment 0.50-0.98%

wherein amounts of said components are on the basis of weightpercentages with respect to a combined total of 100% by weight.
 2. Thepaste flux composition of claim 1 wherein said pigment is aphthalocyanine pigment which changes from colored to colorless at atemperature of approximately 500-600° C.
 3. A process of using a boricacid free paste flux of claim 1 which comprises the step of: adding aphthalocyanine pigment to said flux.
 4. The process of claim 3 whereinsaid step of adding a phthalocyanine pigment effects a color change atan activation temperature of said flux.
 5. The process of claim 4wherein said color change is effected at an activation temperature ofbetween approximately 500-600° C.
 6. A boric acid free paste flux,comprising: a wetting agent in a weight percentage in the range of 0.25to 0.50%; an etchant in a weight percentage in the range of 12.4 to16.8%; an emulsifying agent in a weight percentage in the range of 0.71to 1.35%; potassium tetraborate in a weight percentage in the range of29.5 to 34.8%; potassium fluoroborate in a weight percentage in therange of 29.5 to 34.8%; and pigment in a weight percentage in the rangeof 0.50 to 0.98%; wherein the balance is water.
 7. The boric acid freepaste flux of claim 6, wherein said flux is green in color.
 8. The boricacid free paste flux of claim 6, wherein said flux is fully active inthe temperature range of 566° to 871° C.
 9. The boric acid free pasteflux of claim 6, wherein said etchant is potassium bifluoride.
 10. Theboric acid free paste flux of claim 6, wherein said emulsifying agent isfumed silica.
 11. The boric acid free paste flux of claim 6, whereinsaid pigment is a phthalocyanine pigment.
 12. The boric acid free pasteflux of claim 6, wherein said flux changes color at a temperature withinthe range of approximately 500 to 600° C.